Because CASE (computer aided software engineering) environment is a kind of complex system software, its software architecture is very important. From the viewpoint of software architecture, this paper first presents TBus architectural style, which is a kind of CASE environment architectural style based on ToolBus, then describes the architectural model and system's behavior in formal method, researches and analyzes the corresponding tool structural model. Last the paper implements a TBus architectural instance-LambdaBridge, which proves the validity of ToolBus and TBus architectural styles.